The present invention relates to an electric power transmitting device which transmits electric power in a non-contact manner, a non-contact power supply system which includes the electric power transmitting device, and a control method of the non-contact power supply system, and relates to technology which is effective when applied to an electric power transmitting device utilizing resonant coupling of an electromagnetic field (magnetic resonance), for example.
Practical utilization is advancing in a system using non-contact power transmission which supplies electric power to an electrical machinery and apparatus in a non-contact manner without the intermediary of a power cord, etc. (hereinafter called a “non-contact power supply system”). For example, the well-known non-contact power supply system includes an electromagnetic induction type which utilizes electromagnetic induction between antennae (coils) arranged mutually spaced out, and a magnetic resonance type which utilizes resonant coupling of an electromagnetic field. The NFC (Near Field Communication) specifications are also known as the standards related to non-contact communication technology by which information is transmitted wirelessly. Furthermore, an IC card and a small mobile terminal device in conformity with the NFC specifications are also beginning to spread.
The resonance-type non-contact power supply system is implemented with the use of a resonance circuit including a coil and a capacitor. One of the features is that, compared with the electromagnetic induction type in the past, the resonance-type non-contact power supply system allows long transmission distance between an electric power transmission coil and an electric power reception coil by making Q values of the coils high, and that the resonance-type non-contact power supply system is strong against the displacement between the electric power transmission coil and the electric power reception coil.
In order to realize an efficient non-contact power transmission, it is desirable to transmit electric power by matching the frequency of an electric power transmission signal outputted as the electric power to be transmitted from an electric power transmitting device (hereinafter called “electric power transmission frequency”) and the resonance frequency of a resonance circuit. However, the magnetic resonance type allows transmission in a narrow band region of the frequency characteristic of the coil; therefore, there arises a problem that the resonance frequency of the resonance circuit deviates and the transmission characteristic changes, due to, for example, the change of the parasitic capacitance between windings of the coils by change of the distance between the electric power transmission coil and the electric power reception coil, and due to the influence of a metal part of a housing of the electric power receiving device. Patent Literatures 1 and 2 cited below disclose one of related art technology for realizing efficient non-contact power transmission in the resonance-type non-contact power supply system.
When a resonance frequency of a resonance circuit deviates due to load fluctuation on a receiving side, Patent Literature 1 discloses a technology to cope with the deviation of the resonance frequency, by changing an electric power transmission frequency of the high-frequency power supply to match it with the resonance frequency, and by matching an impedance of a high-frequency power supply on the transmitting side with an input impedance of a transmitting antenna coupled to the high-frequency power supply, by means of a variable impedance circuit.
In order to change or expand the power transmission area which has been restricted to a near range from a transmitting antenna, Patent Literature 2 discloses a technology in which, in a wireless power supply device (a transmitting-side device), the transmitting antenna and plural repeating coils are formed in a sheet shape and arranged in a sheet-shaped main body at the prescribed intervals, where the repeating coils receive and transmit the electric power transmitted from the transmitting antenna in a magnetic resonance relationship.